Work Paper PGECOAGR101
Greenhouse Thermal Curtains
Revision 0
Pacific Gas & Electric Company
Customer Energy Efficiency Department
Greenhouse Thermal Curtains
Measure Code A10
February 5, 2008
At a Glance Summary: Single Layer Thermal Curtains
Applicable Measure Codes:
A10
Measure Description:
Thermal curtains decrease heat losses in greenhouses
(conduction, convection, and radiation losses). Thermal curtains
are installed inside the greenhouse and are typically installed
horizontally near the greenhouse gutter line. It is assumed that
the thermal curtains are deployed during nighttime hours, and
open during daytime hours.
Therms per Square feet
Energy Impact Common Units:
Base Case Description:
Base Case Energy Consumption:
Measure Energy Consumption:
Energy Savings (Base Case – Measure)
Costs Common Units:
Base Case Equipment Cost ($/unit):
Source: PG&E Greenhouse Baseline Study, 2005.
Roof: double-inflated polyethylene with IR inhibiting film.
Wall: single layer polycarbonate
Thermal Curtains: None
Heat setpoint: 55F
Source: PG&E Calculations.
0.374 therms per year
Source: PG&E Calculations.
0.153 therms per year
Source: PG&E Calculations
0.221 therms per year
$ per sq. ft
Effective Useful Life (years):
Source: PG&E Calculations.
$0
Source: PG&E Calculations and manufacturer’s data.
$1.50
Source: PG&E Calculations and manufacturer’s data.
$1.50
Source: DEER. 5 years
Program Type:
Assume Express Efficiency Rebates
Net-to-Gross Ratios:
Source: DEER. 0.96
Important Comments:
Energy consumption and savings are based upon weighted
average for climate zones 1, 2, 3, 4, 5, 11,12, and 13. Results are
extremely sensitive to temperature setpoints for heating. For
example, changing the temperature setpoint from 55F to 80F
increases gas usage by an average of more than 200%. Due to the
enormous variability in conditions needed for various crops, no
attempt was made to capture the variability with additional tiers.
This analysis uses a 55F set point. 1
Measure Equipment Cost ($/unit):
Measure Incremental Cost ($/unit):
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At a Glance Summary: Double Layer Thermal Curtains
Applicable Measure Codes:
Measure Description:
Energy Impact Common Units:
Base Case Description:
Base Case Energy Consumption:
Measure Energy Consumption:
Energy Savings (Base Case – Measure)
Costs Common Units:
Base Case Equipment Cost ($/unit):
For future program enhancement for 2009-2011 program
planning
Double layer thermal curtains decrease heat losses in
greenhouses similarly to single-layer thermal curtains. The
advantage is increased savings and finer control over daytime
light levels.
Therms per Square feet
Source: PG&E Greenhouse Baseline Study, 2005.
Roof: double-inflated polyethylene with IR inhibiting film.
Wall: single layer polycarbonate
Thermal Curtains: None
Heat setpoint: 55F
Source: PG&E Calculations.
0.374 therms per year
Source: PG&E Calculations.
0.093 therms per year
Source: PG&E Calculations
0.281 therms per year
$ per sq. ft
Effective Useful Life (years):
Source: PG&E Calculations.
$0
Source: PG&E Calculations and manufacturer’s data. 2
$2.60
Source: PG&E Calculations and manufacturer’s data.
$2.60
Source: DEER. 5 years
Program Type:
Assume Express Efficiency Rebates
Net-to-Gross Ratios:
Source: DEER. 0.96
Important Comments:
Weighted average for climate zones 1, 2, 3, 4,5, 11,12, and 13
Measure Equipment Cost ($/unit):
Measure Incremental Cost ($/unit):
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Measure
Code
DEER RunID
D03980 1
CFRM00AVHtCtn
D03-980
D03-980
D03-980
D03-980
D03-980
D03-980
CFRM00AVHtCtn
CFRM00AVHtCtn
CFRM00AVHtCtn
CFRM00AVHtCtn
CFRM00AVHtCtn
CFRM00AVHtCtn
Measure Description
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Building
Type
Building
Vintage
Climate
Zone
Peak
Electric
Demand
Reduction
(kW/unit)
AGR
AV
Z01
0
0.064
0.336
$0
$1.50
$1.50
5
AGR
AV
Z01
0
0.080
0.424
$0
$2.60
$2.60
5
AGR
AV
Z02
0
0.046
0.249
$0
$1.50
$1.50
5
AGR
AV
Z02
0
0.064
0.341
$0
$2.60
$2.60
5
AGR
AV
Z03
0
0.044
0.225
$0
$1.50
$1.50
5
AGR
AV
Z03
0
0.056
0.281
$0
$2.60
$2.60
5
AGR
AV
Z04
0
0.042
0.216
$0
$1.50
$1.50
5
AGR
AV
Z04
0
0.056
0.280
$0
$2.60
$2.60
5
AGR
AV
Z05
0
0.037
0.184
$0
$1.50
$1.50
5
AGR
AV
Z05
0
0.046
0.229
$0
$2.60
$2.60
5
AGR
AV
Z11
0
0.039
0.266
$0
$1.50
$1.50
5
AGR
AV
Z11
0
0.049
0.350
$0
$2.60
$2.60
5
AGR
AV
Z12
0
0.043
0.265
$0
$1.50
$1.50
5
Annual
Electric
Savings
(kWh/unit)
Annual Gas
Savings
(therms/unit)
Base
Case
Cost
($/unit)
Measure
Cost
($/unit)
Measure
Incremental
Cost
($/unit)
Effective
Useful
Life
(years)
1
This is the DEER Measure ID
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February 5, 2008
Measure
Code
D03-980
D03-980
DEER RunID
CFRM00AVHtCtn
CFRM00AVHtCtn
Measure Description
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Single-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Double-Layer Greenhouse
Heat Curtain with Infrared
Film (55F setpoint)
Building
Type
Building
Vintage
Climate
Zone
Peak
Electric
Demand
Reduction
(kW/unit)
AGR
AV
Z12
0
0.051
0.348
$0
$2.60
$2.60
5
AGR
AV
Z13
0
0.029
0.191
$0
$1.50
$1.50
5
AGR
AV
Z13
0
0.035
0.251
$0
$2.60
$2.60
5
AGR
AV
Weighted
avg
0
0.042
0.221
$0
$1.50
$1.50
5
AGR
AV
Weighted
avg
0
0.054
0.281
$0
$2.60
$2.60
5
Annual
Electric
Savings
(kWh/unit)
Annual Gas
Savings
(therms/unit)
Base
Case
Cost
($/unit)
Measure
Cost
($/unit)
Measure
Incremental
Cost
($/unit)
Effective
Useful
Life
(years)
:
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February 5, 2008
Work Paper Approvals
Ed Mah
Manager, Forecast, Analysis, and Product Performance
Date
Grant Brohard
Manager, Technical Product Support
Date
Keith Reed or Greydon Hicks
Manager, Mass Market or Target Market
Date
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Document Revision History
Revision #
Revision 0
Date
02/05/08
Description
Greenhouse Thermal Curtains
PGECOAGR101 R0.doc
Author (Company)
Marjorie Stein, Green Building
Studio
Revision 1
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Table of Contents
At a Glance Summary: Single Layer Thermal Curtains ................................................................. ii
At a Glance Summary: Double Layer Thermal Curtains............................................................... iii
Work Paper Approvals................................................................................................................... vi
Document Revision History.......................................................................................................... vii
Table of Contents......................................................................................................................... viii
List of Tables ................................................................................................................................. ix
List of Figures ................................................................................................................................ ix
Section 1. General Measure & Baseline Data................................................................................. 1
1.1 Measure Description & Background: Heat Curtains ............................................................ 1
1.2 DEER Differences Analysis: Heat Curtains ......................................................................... 3
1.3 Codes & Standards Requirements Analysis: Heat Curtains ................................................. 4
1.4 EM&V, Market Potential, and Other Studies ....................................................................... 4
1.5 Base Cases for Savings Estimates: Existing & Above Code................................................ 6
1.6 Base Cases & Measure Effective Useful Lives .................................................................... 6
1.7 Net-to-Gross Ratios for Different Program Strategies.......................................................... 6
Section 2. Calculation Methods ...................................................................................................... 6
2.1 Electric Energy Savings Estimation Methodologies............................................................. 6
2.2. Demand Reduction Estimation Methodologies ................................................................... 9
2.3. Gas Energy Savings Estimation Methodologies .................................................................... 10
Section 3. Load Shapes ................................................................................................................ 10
3.1 Base Cases Load Shapes..................................................................................................... 10
3.2 Measure Load Shapes ......................................................................................................... 10
Section 4. Base Case & Measure Costs ........................................................................................ 10
4.1 Base Case(s) Costs.............................................................................................................. 10
4.2 Measure Costs..................................................................................................................... 10
4.3 Incremental & Full Measure Costs ..................................................................................... 11
Index ............................................................................................................................................. 12
References..................................................................................................................................... 32
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List of Tables
Table 1. Specifications for Ludvig Svensson, Thermal Curtains ................................................... 2
Table 2. Thermal Resistance (R-value) of air gaps......................................................................... 3
Table 3. Use of Thermal Curtains................................................................................................... 4
Table 4. Use of Thermal Curtains, per vendors .............................................................................. 5
Table 5 Net-to-Gross Ratios .......................................................................................................... 6
Table 6. Measure Costs: Single-Layer Heat Curtains................................................................... 11
List of Figures
Figure 1. Graph of Ludvig Svensson XLS Firebreak Energy Curtains. Diffuse Light
Transmission vs Energy Savings Factor. ........................................................................................ 3
Figure 2. Photograph of Ludvig Svensson XLS Firebreak Energy Curtain. .................................. 3
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Section 1. General Measure & Baseline Data
1.1 Measure Description & Background: Heat Curtains
Catalog Description –
Only installations of interior curtains for heat retention in existing gas-heated greenhouses
qualify. The rebate applies to new and retrofit curtain system installations in existing
greenhouses for specific agricultural end-use. Product must be designed by the manufacturer to
be a heat curtain, and the installation must have the ability to automatically or manually move
the curtain into place. Curtain must be located such that the gas heat source provides hot air to
conditioned space bounded by the curtain. Curtain material must have an Energy Savings rating
of >40%, and must have a warranty/product life of 5 years. Include a manufacturer’s
specification sheet documenting type of curtain. Rebate amount is for square foot of curtain
material.
Program Restrictions and Guidelines: Heat Curtains
Terms and Conditions Only installations of interior curtains for heat retention in existing gasheated greenhouses qualify. The rebate applies to new and retrofit curtain system installations in
existing greenhouses for specific agricultural end-use. Product must be designed by the manufacturer
to be a heat curtain, and the installation must have the ability to automatically or manually move the
curtain into place. Curtain must be located such that the gas heat source provides hot air to
conditioned space bounded by the curtain. Curtain material must have an Energy Savings rating of >
40%, and must have a warranty/product life of 5 years. Include a manufacturer’s specification sheet
documenting type of curtain. Rebate amount is for square foot of curtain material. 3
Market Applicability This measure is applicable to agricultural or commercial greenhouses
involved in the production of nursery products, horticultural specialties, or ornamental products.
Technical Description: Single-Layer Heat Curtains
Typically, greenhouse thermal curtains are designed to be placed horizontally above the growing zone
within a greenhouse. Energy is saved in three ways: they trap an insulating air film; the volume of space
requiring heating is reduced; and heat curtains with aluminized strips reflect rising heat back into the
growing zone.
A vendor participating in the PG&E Greenhouse Baseline study explained that there are two basic types
of thermal curtain installations: flat, and slope-flat-slope. The flat is under the gutter level and operates in
a horizontal plane. The slope-flat-slope (or tent) installation is used with some greenhouses that have
other equipment to avoid, or for growers who want to minimize the air trapped above the curtain (or
maximize the area below). Their product is warranted for five years underneath any type of glazing, and
they claim an actual replacement interval of every 7-12 years depending on use, installation quality, etc.
According to Bartok 4 , there are many different materials used as thermal curtains. Porous materials allow
condensation to drain, but are not as effective as nonporous materials in reducing energy use. However,
nonporous curtains could cause the track system to fail if they become too heavy from collected moisture.
Aluminized curtains save about 10% more energy than non-aluminized curtains. The aluminized curtains
are typically a 55% woven white polyester film and double for use as shading. Bartok also refers to
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research conducted in large greenhouses with parallel bays and compares the effectiveness of reflective
curtains facing both directions. The results indicate that outward-facing reflective surface retained heat
slightly better than an inward-facing system.
Table 1. Specifications for Ludvig Svensson, Thermal Curtains 5
Specifications for Ludvig Svensson, Thermal Curtains
(Aluminum/Polyester Strips)
Energy
Diffuse Light
Type
saving
transmission
Calculated, based upon PG&E’s
minimum energy savings requirements
40%
84%
XLS 10 Firebreak
45%
78%
XLS 13 Firebreak
49%
65%
XLS 14 Firebreak
52%
53%
XLS 15 Firebreak
57%
43%
XLS 16 Firebreak
62%
34%
XLS 17 Firebreak
67%
24%
XLS 18 Firebreak
72%
17%
Table 1 presents the specifications for thermal curtains from a large manufacturer. This analysis will
assume the heat curtain has an energy savings factor of 40%, based upon PG&E’s minimal requirement
for qualifying products, with a calculated diffuse light transmission of 84%. The figure below illustrates
the calculations for arriving at the diffuse light transmission of a 40% energy savings factor heat curtain.
LS Svensson XLS Firebreak Heat Curtain Series Diffuse Light
Transmission
85%
80%
75%
70%
65%
Diffuse Light Transmission
60%
55%
50%
45%
40%
35%
30%
25%
20%
y = -2.1975x + 1.7159
15%
10%
5%
0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
Energy Savings Factor
2
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Figure 1. Graph of Ludvig Svensson XLS Firebreak Energy Curtains. Diffuse Light Transmission vs Energy
Savings Factor.
Figure 2. Photograph of Ludvig Svensson XLS Firebreak Energy Curtain.
Technical Description: Double-Layer Heat Curtains
Double-layer heat curtains serve the same purpose as single-layer heat curtains; however, as the name
implies, this system is composed of two independent curtains. The advantage to growers, in addition to
additional energy savings (on the heating side), is the ability to exercise finer control over light levels.
The analysis assumes the double-layer heat curtain system consists of a white acrylic layer of 55% woven
plus a heat curtain with a 40% energy savings factor. The primary benefit of the 40% energy savings
factor heat curtain is radiant heat retention. The primary benefit of the acrylic layer is an added air film to
trap heat. This analysis assumes a 12-inch air gap between the two layers of heat curtain. Without an air
gap the added benefit of the two layers is greatly reduced. Conductance (u-value) of the 40% energy
savings factor heat curtain is 1-0.40 = 0.60. R-value is 1/0.60 = 1.67. R-value of air-film between two
layers of heat curtains is approximately 2.5. Total R-value is 4.17. U-value of 0.240 is used as a multiplier
on the roof glazing conductance to model heat retention during the night.
Table 2. Thermal Resistance (R-value) of air gaps. 6
air gap (inches)
R-value
0.5
1.6
0.75
1.7
1.5
1.8
3.5
2.0
12
2.5
18
3.0
1.2 DEER Differences Analysis: Heat Curtains
The DEER Measure ID D03-981 Greenhouse Heat Curtain 7 is based upon a prototypical 4,000 square
foot greenhouse facility with average characteristics for SoCalGas customer participants for Express
Efficiency heat curtain measures during PY 2001. This is per section 4.2 of the DEER Update Study Final
Report. The results for this measure are sensitive to weather and extremely sensitive to temperature
setpoints. The estimated savings from the DEER study is 0.39 therms/square foot.
The incremental cost cited by DEER ($0.49) is much lower than that cited by vendors in the 2005
Greenhouse Baseline Study conducted by PG&E ($1.50 for single-layer).
The useful life of 5 years is approximately what vendors also cite.
DEER does not analyze double-layer heat curtains.
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1.3 Codes & Standards Requirements Analysis: Heat Curtains
Greenhouses and the heat curtains measures are not governed by either state or federal codes and
standards.
Title 20: These measures do not fall under Title 20 of the California Energy Regulations.
Title 24: These measures do not fall under Title 24 of the California Energy Regulations.
Federal Standards: These measures do not fall under Federal DOE or EPA Energy Regulations.
1.4 EM&V, Market Potential, and Other Studies
M&V Group to Provide appropriate report(s)
Based upon the PG&E Greenhouse Baseline Study (pages 26-27), the use of heat curtains is not standard
practice for greenhouses within PG&E’s service territory. The study interviewed 22 greenhouse owners.
A frequent comment from greenhouse owners regarding thermal curtains is that they would love to use
them, but price is a limiting factor. Some reported taking advantage of past PG&E incentives to purchase
thermal curtains, stating that they would not have made the purchase without incentives. Seven of the 21
greenhouse owners participating in the study reported using no thermal curtains at all. Ten of the
facilities use them on some portion of their greenhouses (one facility uses thermal curtains on less than
one percent of the space and complained of the mechanism never functioning satisfactorily). The
remaining four use thermal curtains on most or all of their greenhouses. In all cases the thermal curtains
serve as a shade-cloth as well. Other comments regarding thermal curtains are:
• would love to have but never seem to have enough $ for investments in energy improvements
• too expensive
• don't feel it's needed
• too expensive, 15 yrs ago PG&E offered incentives but didn't think it was enough, would be nice
to have energy curtains
• too expensive
• expensive, thinks >$1/sq ft but not sure how much more. Used PG&E rebate on last purchase
• used in about 15% of houses, wishes he could use more but is expensive
• used in about 40% of houses, would use more but cost is factor
• older houses not set up for it
Table 3. Use of Thermal Curtains
Bin
TOTAL
Never
Use
7
Rarely
Use
1
Sometimes
Use
9
Typically
Use
4
Fourteen of the greenhouses have some thermal curtains installed. In one case the mechanism doesn’t
work properly. In four additional cases, only the newer houses have them installed and the old houses are
not set up for the mechanism to be installed. Because only three of the owners use thermal curtains in
100% of the houses it appears that the use of thermal curtains is not a standard practice. In all cases the
use of the thermal curtains doubled as shade cloth.
In general, the vendors and consultants indicated that shade cloths used independently from thermal
curtains were not that common and are not as good as thermal curtains. However, the thermal curtains
that double as shade cloths are fairly common, according to two of the vendor/consultants. Two more
indicate that these systems used to be more common than they are now. One other indicated that he
thought foliage growers sometimes used them. These mixtures of answers seem consistent with the
greenhouse owners as well. Generally it seems that thermal curtains are not a standard baseline in
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California greenhouses and their installation is heavily dependent upon incentives to offset the initial
expense.
Another vendor commented that if there is an incentive, more growers tend to invest in thermal curtains.
He went on to estimate that California greenhouse growers who may invest in energy curtains without the
rebate available when planning new construction break down as:
• Approximately 50% of the glass house growers
• 25% of the rigid plastic growers
• 5-10% of the poly house growers.
He speculated the possible reasons for low numbers of poly house growers installing thermal curtains
probably had to do with the fact that these structures are more energy efficient in most cases, and also
they tend to be the low-cost options and thermal curtains are expensive. Additional comments from the
vendors are on the following table:
Table 4. Use of Thermal Curtains, per vendors
How Common are Thermal Curtains
sometimes used--especially among foliage growers
very common. Uses LS aluminized products with 55% shade. Cost $1.25-$1.30/sq ft mostly just applied to
ceiling at gutter height.
Very common to use aluminized energy curtains for both shade & heat retention. Typical open at dawn, close at
10am in summer to cut heat (mfg claims 50% of btus), open later afternoon, close at sunset. Cost $1.50-$2.00/sq
ft
all else being equal, good curtains are best investment, save 30-40% on heat and allow more control over when
crops mature by controlling sunlight
fairly common with dual function shade cloth. Estimates cost at $1.55/sf for complete system.
same as shade cloths
Not very common, need complicated pulleys and controls. Very expensive.
too expensive
Delta Therms Assumption (ΔT): Source: PG&E Calculations.
Baseline therms usage: 0.374 therms/square foot.
Single-Layer heat curtains: 0.153 therms/square foot.
Double-Layer heat curtains: 0.093 therms/square foot.
Net-to-Gross Assumption: 0.96. Source: DEER value, assumes Express Efficiency Rebates program.
In-service factor/first year installation rate: From the PG&E Greenhouse Baseline Study (page 26). 8
“A frequent comment from greenhouse owners regarding thermal curtains is that they would love to use
them, but price is a limiting factor. Some reported taking advantage of past PG&E incentives to purchase
thermal curtains, stating that they would not have made the purchase without incentives. Seven of the 21
(33%) greenhouse owners participating in the study reported using no thermal curtains at all. Ten of the
facilities (46.7%) use them on some portion of their greenhouses (one facility uses thermal curtains on
less than one percent of the space and complained of the mechanism never functioning satisfactorily). The
remaining four (19%) use thermal curtains on most or all of their greenhouses.”
Hours of Operation: From the PG&E Greenhouse Baseline Study (page 50 9 ).
The interviews with the greenhouse owners revealed that while many crops are seasonal in nature, the
greenhouses rarely sit idle. Crops are usually rotated through the nursery during the entire year. Based
upon this finding, the baseline schedule of operations will be assumed to be 24-hours per day, 7 days per
week.
Effective Useful Life: 5 years. Source: DEER.
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1.5 Base Cases for Savings Estimates: Existing & Above Code
The base case for the single-layer heat curtains measure is no heat curtain.
The base case for the double-layer heat curtains measure is no heat curtain.
No state or federal codes apply to either of these measures.
1.6 Base Cases & Measure Effective Useful Lives
Based upon DEER data an effective useful life of five years is assumed for both single-layer and doublelayer heat curtains. DEER source 2004-05, Version 2.01 -- Measure ID D03-0980.
1.7 Net-to-Gross Ratios for Different Program Strategies
The Net-to-Gross (NTG) ratios are estimated based on whole energy efficiency program approaches and
strategies. They are summarized in the CPUC Energy Efficiency Policy Manual and on the DEER web
site. This section should discuss the possible program strategies applicable to the measure and indicate
the NTG ratio for each from approved sources. If there are new EM&V studies with more recent NTG
estimates, they may be cited here.
Table 1 below summarizes all applicable Net-to-Gross ratios for programs that may be used by this
measure.
Table 5 Net-to-Gross Ratios
Program Approach
NTG
Name of Program
Section 2. Calculation Methods
2.1 Electric Energy Savings Estimation Methodologies
A computer simulation model has been developed using eQUEST™ and Quickee™. These programs are
Windows™ applications that act as interfaces to the DOE 2.2 hourly energy simulation engine. DOE-2.2
was developed by the U.S. Department of Energy and J.J. Hirsch and Associates, specifically for
evaluating the energy performance of commercial and residential buildings, and has been widely
reviewed and validated in the public domain. DOE-2.2 calculates hour-by-hour building energy
consumption over an entire year (8760 hours) using weather data for the location under consideration.
eQUEST is a graphical user interface to DOE-2.2 developed by J.J. Hirsch and Associates and others.
Quickee is a free utility, which allows a user to use Microsoft Excel to control the input and output of
parametric DOE-2 runs.
Input to the program consists of a detailed description of the building being analyzed, including glazing
specifications, cooling and heating systems, hourly scheduling of equipment, and thermostat settings.
The baseline greenhouse building consists of the following features:
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Roofs: Double-inflated poly 10 without IR film (U-value 0.70, Visible Transmittance 0.78, and Shading
Coefficient 0.85). Or single-layer polycarbonate (U-value 1.14, Visible Transmittance 0.83, Shading
Coefficient 0.85.
Walls: Single layer polycarbonate: U-value 1.14, R-Value 0.91, Visible Transmittance 0.90, Shading
Coefficient 1.00.
Floors: Uninsulated bare soil
Thermostats: Temperature sensors are assumed to be located at crop level (approximately four feet
above the floor) near the middle of each greenhouse range. Baseline heaters are assumed to be located
overhead. The location of the heating systems causes stratification, with the air above the gutter level 7 to
10º F hotter than at the thermostat level, per John Hoogenboom, a greenhouse consultant 11 . Since the
eQUEST computer model cannot account for thermal stratification of air, the thermostat schedules are
modified to account for stratification effects by adding a temperature offset. This strategy has been
borrowed from the one utilized by Marlin Addison, an eQUEST expert, and Hoogenboom. 12 An assumed
space temperature offset of 7.5º F is recommended without heat curtains and 4º F with heat curtains.
Heating: The baseline heating system in California greenhouses consists of overhead gas-fired unit
heaters with an 80% heating efficiency.
Cooling: For coastal areas, the baseline cooling system is passive natural ventilation with ridge & vent
design (upper vents sized at 20% of floor area, lower vents same size). For inland valley areas the
baseline cooling system is fan and pad. This evaporative cooling system is assumed to be 80% efficient.
Fans and Airflow: For the non-coastal areas, exhaust fans are simulated to provide 60 air changes per
hour of ventilation whenever the greenhouse temperature exceeds 75 F. Based upon Energy Conservation
for Commercial Greenhouses, it is assumed that the target rate is eight CFM/square foot, and the fans are
assumed to deliver 20,000 cfm per hp. For coastal locations, no exhaust fans are assumed in the baseline
model—only passive natural ventilation.
Horizontal airflow fans are used to mix the air and reduce mold and mildew growth when the greenhouse
is being ventilated. The model assumes HAF fans with a capacity of 0.25 cfm, based upon
recommendations from Energy Conservation for Commercial Greenhouses for greenhouses.
Lighting: No supplemental lighting has been assumed in the analysis.
Infiltration: A rate of 1.1 air changes per hour is assumed in the model. Energy Conservation for
Commercial Greenhouses cites an average of 0.75 – 1.5 air changes per hour for new Construction glass,
fiberglass, polycarbonate, or acrylic sheets:
Orientation: According to Energy Conservation for Commercial Greenhouses 13 , locations above 40°N
latitude should have the ridge of multi-span greenhouses running north to south, and the ridge of single
bay greenhouses running east to west. All houses below 40°N should have the ridges running north to
south to optimize the light.
Schedule: 24 hours per day, 7 days per week.
Utility Rates: Assumes PG&E’s AG-5 rate for electricity and GNR-1 rate for gas.
Single Heat Curtain System: Assumes a heat curtain with a 40% energy savings factor. Conductance (uvalue) is 1-0.40 = 0.60. U-value of 0.60 is used as a multiplier on the roof glazing conductance to model
heat retention during the night.
Double Heat Curtain System: Assumes white acrylic layer, 55% woven plus a heat curtain with a 40%
energy savings factor. Primary benefit of the 40% energy savings factor heat curtain is radiant heat
retention. The primary benefit of the acrylic layer is an added air film to trap heat. This analysis assumes
a 12-inch air gap between the two layers of heat curtain. Without an air gap the added benefit of the two
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layers is greatly reduced. Conductance (u-value) of the 40% energy savings factor heat curtain is 1-0.40 =
0.60. R-value is 1/0.60 = 1.67. R-value of air-film between two layers of heat curtains is approximately
2.5. Total R-value is 4.17. U-value of 0.240 is used as a multiplier on the roof glazing conductance to
model heat retention during the night.
∆Watts/unit: Heat curtain measures have no demand savings.
Annual Electric Savings:
Energy Savings [kWh/Unit] =
Single-layer Heat Curtain: 0.042 kWh/square foot
Double-layer Heat Curtain: 0.054 kWh/square foot
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Greenhouse Structure
8' - 0''
unit heater
16' - 0''
thermal curtain
32' - 0''
Wall height
16.0 ft
=
16' - 0''
Width
32.0 ft
=
32' - 0''
Roof length
17.9 ft
=
17' - 11''
Attic height
8.0 ft
=
8' - 0''
Description
Design
gutter connected bays with hoop roofs
Roof Material
double inflated PE with IR film
Wall Material
single layer polycarbonate
Floor
uninsulated bare soil
Thermal Curtain Position
truss to truss at gutter height
Thermal Curtain Operation
deployed when temperature falls below 65F
Surface Area and Volume Calculations
Dimensions
Number of Bays
14
Width (each bay)
ft
Wall Height (each bay)
ft
16
Length
ft
256
Peak Height (gutter to peak)
ft
8.0
Roof Width (gutter to peak)
ft
17.9
Roof Pitch, rise to run (x in 12)
32
6.0
Surface Area
Side Walls
ft2
8,192
End Wall (without gable)
ft
2
14,336
Total Wall (below gutter)
ft
2
22,528
End Gable
ft
Roof
ft
Floor
ft
2
3,584
2
128,225
2
114,688
3
2,293,760
Interior Volume
Total
ft
Gable (above gutter)
ft
Main (below gutter)
ft
3
458,752
3
1,835,008
2.2. Demand Reduction Estimation Methodologies
There is no anticipated demand reduction associated with this measure.
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2.3. Gas Energy Savings Estimation Methodologies
See section 2.1 for the methodology.
Annual Gas Savings:
Baseline therms usage: 0.374 therms/square foot.
Single-Layer heat curtains: 0.153 therms/square foot.
Double-Layer heat curtains: 0.093 therms/square foot.
Section 3. Load Shapes
Load Shapes are an important part of the life-cycle cost analysis of any energy efficiency program
portfolio. The net benefits associated with a measure are based on the amount of energy saved and the
avoided cost per unit of energy saved. For electricity, the avoided cost varies hourly over an entire year.
Thus, the net benefits calculation for a measure requires both the total annual energy savings (kWh) of the
measure and the distribution of that savings over the year. The distribution of savings over the year is
represented by the measure’s load shape. The measure’s load shape indicates what fraction of annual
energy savings occurs in each time period of the year. An hourly load shape indicates what fraction of
annual savings occurs for each hour of the year. A Time-of-Use (TOU) load shape indicates what
fraction occurs within five or six broad time-of-use periods, typically defined by a specific utility rate
tariff. Formally, a load shape is a set of fractions summing to unity, one fraction for each hour or for each
TOU period. Multiplying the measure load shape with the hourly avoided cost stream determines the
average avoided cost per kWh for use in the life cycle cost analysis that determines a measure’s Total
Resource Cost (TRC) benefit.
3.1 Base Cases Load Shapes
The base case load shape would be expected to follow a typical (residential or non-residential) (end use
name) end use load shape.
3.2 Measure Load Shapes
For purposes of the net benefits estimates in the E3 calculator, what is required is the load shape that
ideally represents the difference between the base equipment and the installed energy efficiency measure.
This difference load profile is what is called the Measure Load Shape and would be the preferred load
shape for use in the net benefits calculations.
The measure load shape for this measure is determined by the E3 calculator based on the applicable
(residential or non-residential) market sector and the (end-use name) end-use.
Section 4. Base Case & Measure Costs
4.1 Base Case(s) Costs
There is no cost associated with the base case since the base case is no heat curtain.
4.2 Measure Costs
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The single-layer heat curtain measure cost is $1.50 per square foot. This includes materials and full
installation costs. The source of the cost is previous studies and manufacturer’s data (taken from the
PG&E Greenhouse Baseline Study):
Table 6. Measure Costs: Single-Layer Heat Curtains
Life
(years)
5
Installed Cost
per sq. ft.
Source
Greenhouse Thermal Curtains and
Infrared Films
Workpaper for PY2006-2008
prepared for Southern California Gas
Co. by Energy and Environmental
$1.50
Analysis, Inc. (B-REP-06-599-17B)
10
$1.51
Notes
September
2006
2001
Cost depends on size of greenhouse, blanket
material, and type of track / drive system
used.
$1.00-$3.00
John Hoogenbom
Scott Sanford, Reducing Natural Gas
/ Propane use for Greenhouse Space
Heating
John W. Bartok, Energy
Conservation for Commercial
Greenhouses
2001
lower price is for larger areas of 20,000 sq ft
or more
$1.10-$1.40
Kurt Parbst, Ludvig Svensson
Nov. 2005
For large installations > 1 acre.
$1.10 to
$3.35
5-12
Date
Nov. 2003
The double-layer heat curtain measure cost is $2.60 per square foot. This includes materials and full
installation costs. The source of the cost is manufacturer’s data: Per Peter Fryn of System USA Inc.
indicated that a tented, double system would cost $2.60 and a double flat system would cost $2.10
installed
4.3 Incremental & Full Measure Costs
In the case of heat curtains, because the baseline is no heat curtains (and therefore no cost), the
incremental costs are identical to the full measure costs.
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Index
Heat Curtain
Thermal Curtain
Heat Blanket
Thermal Blanket
Greenhouse
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Naming Convention for Workpaper Codes.
End Use
Code
Refrigeration
REF
Agriculture
AGR
Appliances (not food Service) APP
Food Service
FST
Domestic Hot Water
DHW
HVAC (including HVAC
HVC
water heat)
Computers
COM
Process Loads (not HVAC or
PRO
DHW
Building Shell
BLD
Lighting
LTG
Pumping
PUM
Number variations
Gas 10X Electric 20X
Gas 10X Electric 20X
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Appendix
This appendix is a copy of January 11, 2008 memo to PG&E, which outlines the results of analysis for
several different tiers, the bases for the weighted averages, and other details.
Hello Charlene,
TO:
Charlene Spoor, PG&E Sr. Program Engineer
Kathy Burney, PG&E
Chris Li , PG&E RAS Program Engineer
CC:
Charlie Middleton, P.E., PG&E Senior Chemical Engineer
John Blessent, PG&E Sr. Program Engineer
PHONE: 415-973-0747
RE:
FROM:
Marjorie Stein
PAGES:
17
DATE:
January 11, 2008
Greenhouse Deemed Savings Analysis: Initial Results
This memo summarizes the initial results of greenhouse modeling for PG&E’s Deemed Savings Program.
The purpose of this memo is to help PG&E make decisions regarding the number of tiers to offer for the
Deemed Savings Program for Heat Curtains and IR Film for Greenhouses.
Table of Contents
Table of Contents........................................................................................................................... 14
Recommendations for Heat Curtain and IR Film for Greenhouse Tiers ....................................... 15
Simulation Model Baseline............................................................................................................ 19
Results............................................................................................................................................ 22
Appendix........................................................................................................................................ 24
Baseline Roof Material .............................................................................................................. 24
Climate Zones............................................................................................................................ 25
Electricity Savings ..................................................................................................................... 30
Table 1. Summary of Recommended Tiers, Annual Natural Gas Use and Savings (Therms/Square
Foot)................................................................................................................................................... 15
Table 2. Annual Natural gas savings (therms per square foot ) with addition of Single-layer Heat
Curtain. Location versus Roof material............................................................................................. 16
Table 3. Proposed Grouping of Greenhouses by Climate Zones for the Deemed Savings Program. 16
Table 4. Annual Natural gas savings (per square foot ) with IR Film. Location versus Temperature
Setpoint .............................................................................................................................................. 17
Table 5. Proposed Tiers for the Greenhouse Deemed Savings Program: IR Inhibiting Film. .......... 17
Table 6. Proposed Tiers for the Greenhouse Deemed Savings Program: Heat Curtains. ................. 17
Table 7. Greenhouse Deemed Savings Modeling Matrix.................................................................. 18
Table 8. Thermal Resistance (R-value) of air gaps. .......................................................................... 21
Table 9. Specifications for Ludvig Svensson, Thermal Curtains ...................................................... 21
Table 10. Annual Natural Gas Usage and Savings (therms per square foot) .................................... 23
Table 11. Grouping of Greenhouses by Climate Zones for the PG&E Greenhouse Baseline Study.25
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Table 12. Proposed Grouping of Greenhouses by Climate Zones for the Deemed Savings Program.
........................................................................................................................................................... 26
Table 13. Summary of California Energy Commission Climate Zone HDD Calculations............... 26
Table 14. Square Footage of Greenhouses by County and Climate Zones. ...................................... 29
Table 15. Electricity Use and Savings Results .................................................................................. 31
Figure 1. Comparison of Gas Savings for Single-Layer Heat Curtains added to Various Roof
Baselines. ........................................................................................................................................... 16
Figure 2. Distribution of Greenhouse Roof Materials (Source: PG&E Greenhouse Baseline Study)
........................................................................................................................................................... 24
Figure 3. Graph of Ludvig Svensson XLS Firebreak Energy Curtains. Diffuse Light Transmission
vs Energy Savings Factor. ................................................................................................................. 25
Figure 4. Monthly Minimum Temperatures ...................................................................................... 27
Figure 5. Allocation of greenhouse square footage, coastal climate zones. ...................................... 27
Figure 6. Allocation of greenhouse square footage, inland climate zones. ....................................... 28
Figure 7. Allocation of greenhouse square footage, all climate zones. ............................................. 28
Figure 8. California Climate Zones Map.......................................................................................... 30
Recommendations for Heat Curtain and IR Film for Greenhouse Tiers
The following table summarizes our recommendations for PG&E’s Deemed Savings program for
Greenhouse Heat Curtains and IR Film. The tiers include six baselines with annual natural gas savings shown
relative to the appropriate baseline. For example, “Double-inflated polyethylene no IR film” at 55F has an
annual natural gas usage of 0.47 therm per square foot; adding a single-layer heat curtain to this baseline
results in an annual gas savings of 0.29 therms per square foot; while the use of a double-layer heat curtain
saves 0.39 therms per square foot, relative to the “No Heat Curtain” baseline.
Use
Roof Material
Interior
Temp
Setpoint (F)
No Heat
Curtain
(baseline)
Single
Layer Heat
Curtain
Savings
DoubleLayer
Heat
Curtain
IR Film
55
0.71
0.40
0.55
N/A
Polycarbonate single layer
80
3.42
0.86
1.53
N/A
Double-inflated polyethylene no IR film
55
80
0.47
2.62
0.29
0.75
0.39
1.25
0.13
0.49
Double-inflated polyethylene with IR Film
55
80
0.34
2.14
0.22
0.66
0.28
1.03
N/A
N/A
Table 7. Summary of Recommended Tiers, Annual Natural Gas Use and Savings (Therms/Square Foot)
Because greenhouse measures are very sensitive to heating temperature setpoints, it is recommended that, at
a minimum, PG&E tier the incentives by temperature setpoints (80F for orchids and 55F for all other crops.).
We also recommend differentiating single-layer baseline roofs versus double-layer baseline roofs. We do not
recommend PG&E tier the incentives by climate zones because the overwhelming majority of greenhouse
square footage is in climate zone 3 (nearly 48%--see Figure 9) and the results are more sensitive to interior
temperature setpoints and roof material than they are to climate zones.
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The analysis indicates that while the natural gas savings are sensitive to weather, the results are more
sensitive to baseline roof materials. For example, in Table 8 there is a 19% difference in the annual natural
gas savings between the coastal versus inland location when adding a single-layer heat curtain to a doubleinflated polyethylene roof with IR film. However; the difference in natural gas savings between adding a
single-layer heat curtain to a double-inflated polyethylene roof with IR film versus a single-layer
polycarbonate roof, both in a coastal location, is 84%. The results are also displayed in Figure 3.
Double-Inflated
Polyethylene with IR
Film
Double-Inflated
Polyethylene without
IR Film
Single-Layer
Polycarbonate
%
Difference
0.21
0.29
0.39
84%
75%
Coastal weighted average (55F)
Inland (weighted average (55F)
0.25
0.32
0.45
% Difference
19%
11%
13%
Table 8. Annual Natural gas savings (therms per square foot ) with addition of Single-layer Heat Curtain.
Location versus Roof material.
Annual Natural Gas Savings (Therms/sq ft)
Comparison of Savings: Single Heat Curtain added to Different
Baseline Roofs
0.50
0.45
0.40
0.35
Double-Inflated
Polyethylene with IR Film
0.30
0.25
Double-Inflated
Polyethylene without IR
Film
Single-Layer Polycarbonate
0.20
0.15
0.10
0.05
0.00
Coastal weighted average
(55F)
Inland (weighted average
(55F)
Figure 3. Comparison of Gas Savings for Single-Layer Heat Curtains added to Various Roof Baselines.
If PG&E wishes to tier the deemed savings by location, we propose, for the sake of simplicity, aggregating
the climate zones into two categories: coastal (climate zones 1, 2, 3, 4 and 5) and inland (climate zones 11,
12, and 13). See the appendix for details.
Climate Zones
1, 2, 3, 4, and 5
11 12, and 13
Category
Coastal
Inland
Table 9. Proposed Grouping of Greenhouses by Climate Zones for the Deemed Savings Program.
While there is a significant difference in savings with applying heat curtains between double-inflated roofs
with and without IR film (see Figure 3), it is recommended that PG&E not adopt a separate tier for these two
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cases. This recommendation is based upon the findings of the Greeenhouse Baseline Study that the majority
of greenhouse roofs consist of double-inflated polyethylene with IR film (see Figure 4 in the appendix).
While this study was based upon a small sample size (22 greenhouse facilities), the findings are backed up by
anecdotal information from the vendors. Additionally, polyethylene roofs have a very short life-span (3-5
years) compared to polycarbonate or acrylic (10-20+ years). By using the improved double-polyethylene
with IR film baseline for heat curtains incentives, PG&E could avoid incenting a more generous amount for a
roof which may be replaced within a few years.
Table 10 outlines how the savings realized with the addition of IR inhibiting film to double-inflated
polyethylene is much more sensitive to the greenhouse temperature setpoint than the location. For example,
with a 55F setpoint, there is only a 14% difference in the annual natural gas savings between the coastal
versus the inland greenhouse. However; there is a difference of 276% in savings between a 55F versus a 80F
temperature setpoint for a coastal greenhouse.
55F Setpoint
80F Setpoint
% Difference
0.13
0.49
276%
Inland (weighted average (55F)
0.15
0.45
203%
% Difference
14%
8%
Coastal weighted average (55F)
Table 10. Annual Natural gas savings (per square foot ) with IR Film. Location versus Temperature Setpoint
The following table summarizes the two proposed tiers for greenhouse deemed savings incentives for IR
inhibiting film: 55F setpoint and 80F setpoint.
Baseline Location
Weighted Average of All
Locations
Baseline Temperature Setpoint
Baseline Roof Material
Measure
Double-inflated polyethylene
IR inhibiting film
55F for all other Crops
80F for Orchids
Table 11. Proposed Tiers for the Greenhouse Deemed Savings Program: IR Inhibiting Film.
Baseline
Location
Weighted
Average of
All
Locations
Baseline
Temperature
Setpoint
55F for all other
Crops
80F for Orchids
Baseline Roof Material
Measure
Double-inflated polyethylene w/ IR
inhibiting film
Single Layer Heat Curtain
2nd Layer Heat Curtain added to existing Heat Curtain
Single Layer Heat Curtain
2nd Layer Heat Curtain added to existing Heat Curtain
Single Layer Heat Curtain
2nd Layer Heat Curtain added to existing Heat Curtain
Single Layer Heat Curtain
2nd Layer Heat Curtain added to existing Heat Curtain
Single layer polycarbonate
Double-inflated polyethylene with IR
inhibiting film
Single layer polycarbonate
Table 12. Proposed Tiers for the Greenhouse Deemed Savings Program: Heat Curtains.
Table 13 summarizes the modeling scenarios investigated for this initial analysis. As can be seen, analysis
was carried out for the double-inflated polyethylene roofs both with and without IR inhibiting film for
baselines. Additionally, as discussed, analysis was carried out for assuming a 30% production increase with
the use of double heat curtains. This production increase is based upon a conversation with Andy Matsui of
Matsui Nursery.
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Modeling Scenarios
Climate
Zone
Roof Material
Polycarbonate single layer
California
Coastal
Climate
Double-inflated polyethylene
Double-inflated polyethylene
with IR Film
Polycarbonate single layer
California
Inland
Climate
Double-inflated polyethylene
Double-inflated polyethylene
with IR Film
Interior
Temp
Setpoint
(F) 2
No Heat Curtain
Single
Layer Heat
Curtain
Single layer
Heat Curtain
added to
Existing
Heat Curtain
Double heat
curtains +
30%
production
increase
IR Film
55
X (baseline)
X
X
X
N/A
80
X (baseline)
X
X
X
N/A
55
X (baseline)
X
X
X
X
80
X (baseline)
X
X
X
X
55
X (baseline)
X
X
X
N/A
80
X (baseline)
X
X
X
N/A
55
X (baseline)
X
X
X
N/A
80
X (baseline)
X
X
X
N/A
55
X (baseline)
X
X
X
X
80
X (baseline)
X
X
X
X
55
X (baseline)
X
X
X
N/A
80
X (baseline)
X
X
X
N/A
Table 13. Greenhouse Deemed Savings Modeling Matrix
2
The recommended heating setpoint is 55F for Gerbera, a common floral crop. Orchid crops are kept at approximately 80F.
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Simulation Model Baseline
Greenhouse Structure
8' - 0''
unit heater
16' - 0''
thermal curtain
32' - 0''
Wall height
16.0 ft
=
16' - 0''
Width
32.0 ft
=
32' - 0''
Roof length
17.9 ft
=
17' - 11''
Attic height
8.0 ft
=
8' - 0''
Description
Design
gutter connected bays with hoop roofs
Roof Material
double inflated PE with IR film
Wall Material
single layer polycarbonate
Floor
uninsulated bare soil
Thermal Curtain Position
truss to truss at gutter height
Thermal Curtain Operation
deployed when temperature falls below 65F
Surface Area and Volume Calculations
Dimensions
Number of Bays
14
Width (each bay)
ft
Wall Height (each bay)
ft
16
Length
ft
256
Peak Height (gutter to peak)
ft
8.0
Roof Width (gutter to peak)
ft
17.9
Roof Pitch, rise to run (x in 12)
32
6.0
Surface Area
Side Walls
ft2
8,192
2
14,336
2
22,528
End Wall (without gable)
ft
Total Wall (below gutter)
ft
End Gable
ft
Roof
ft
Floor
ft
2
3,584
2
128,225
2
114,688
3
2,293,760
Interior Volume
Total
ft
Gable (above gutter)
ft
Main (below gutter)
ft
3
458,752
3
1,835,008
The baseline greenhouse building consists of the following features:
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Roofs:
Double-inflated poly 3 without IR film (U-value 0.70, Visible Transmittance 0.78, and Shading
Coefficient 0.85 4 ).
Double-inflated poly with IR film (U-value 0.50, Visible Transmittance 0.78, and Shading
Coefficient 0.85).
Single-layer polycarbonate (U-value 1.14, Visible Transmittance 0.83, Shading Coefficient 0.85.
Walls: Single layer polycarbonate: U-value 1.14, R-Value 0.91, Visible Transmittance 0.90, Shading
Coefficient 1.00.
Floors: uninsulated bare soil
Thermostats: Temperature sensors are assumed to be located at crop level (approximately four feet above
the floor) near the middle of each greenhouse range. Baseline heaters are assumed to be located overhead.
The location of the heating systems causes stratification, with the air above the gutter level 7 to 10º F hotter
than at the thermostat level, per Hoogeboom. Since the eQUEST computer model cannot account for
thermal stratification of air, the thermostat schedules are modified to account for stratification effects by
adding a temperature offset. This strategy has been borrowed from the one utilized by Marlin Addison, an
eQUEST expert, and John Hoogenboom, a greenhouse consultant. An assumed space temperature offset of
7.5º F is recommended without heat curtains and 4º F with heat curtains.
Heating: The baseline heating system in California greenhouses consists of overhead gas-fired unit heaters
with an 80% heating efficiency. .
Cooling: For coastal areas, the baseline cooling system is passive natural ventilation with ridge & vent
design (upper vents sized at 20% of floor area, lower vents same size ). For inland valley areas the baseline
cooling system is fan and pad. This evaporative cooling system is assumed to be 80% efficient.
Fans and Airflow: For the non-coastal areas, exhaust fans are simulated to provide 60 air changes per hour
of ventilation whenever the greenhouse temperature exceeds 75 F. Based upon Energy Conservation for
Commercial Greenhouses, it is assumed that the target rate is eight CFM/square foot, and the fans are
assumed to deliver 20,000 cfm per hp. For coastal locations, no exhaust fans are assumed in the baseline
model—only passive natural ventilation.
Horizontal airflow fans are used to mix the air and reduce mold and mildew growth when the greenhouse is
being ventilated. The model assumes HAF fans with a capacity of 0.25 cfm, based upon recommendations
from Energy Conservation for Commercial Greenhouses for greenhouses.
Lighting: No supplemental lighting has been assumed in the analysis.
Infiltration: A rate of 0.75 air changes per hour is assumed in the model. Energy Conservation for
Commercial Greenhouses cites an average of 0.5 – 1.0 air changes per hour for greenhouse construction:
Orientation: According to Energy Conservation for Commercial Greenhouses, locations above 40°N
latitude should have the ridge of multi-span greenhouses running north to south, and the ridge of single bay
3
Peter Fryn of System USA inc. is a major vendor to greenhouse owners. His experience is that the baseline roof material for coastal
greenhouses is single-layer Dynaglas (Polycarbonate) and not double-inflated polyethylene. Our 2005 baseline study for PG&E
found that of the 22 greenhouse facilities in coastal locations interviewed for the study, the largest number (7) had doublepolyethylene roofs, 5 had glass roofs, and 3 had single polycarbonate roofs. The remaining roof types were distributed among other
materials.
4
Our original greenhouse baseline study for PG&E published in 2005 used a shading coefficient for double-inflated polyethylene
film of 0.28—this is a reasonable proxy when taking into account the energy absorption of plants. We have subsequently revised our
methodology to separate out the energy absorption of plants and utilize a shading coefficient value of 0.85 (Source: Aldrich, Robert
A. and Bartok, John W., Jr. 1994. Greenhouse Engineering. NRAES-33. Ithaca, NY: Natural Resource, Agriculture, and Engineering
Service.)
20
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greenhouses running east to west. All houses below 40°N should have the ridges running north to south to
optimize the light..
Schedule: 24 hours per day, 7 days per week.
Utility Rates: Assumes PG&E’sAG-5 rate for electricity and GNR-1 rate for gas.
Single Heat Curtain System: Assumes a heat curtain with a 40% energy savings factor. Conductance (uvalue) is 1-0.40 = 0.60. U-value of 0.60 is used as a multiplier on the roof glazing conductance to model heat
retention during the night.
Double Heat Curtain System: Assumes white acrylic layer, 55% woven plus a heat curtain with a 40%
energy savings factor. Primary benefit of the 40% energy savings factor heat curtain is radiant heat retention.
The primary benefit of the acrylic layer is an added air film, which trap heat. This analysis assumes a 12-inch
air gap between the two layers of heat curtain. Without an air gap the added benefit of the two layers is
greatly reduced. Conductance (u-value) of the 40% energy savings factor heat curtain is 1-0.40 = 0.60. Rvalue is 1/0.60 = 1.67. The R-value of air-film between two layers of heat curtains is approximately 2.5.
Total R-value is 4.17. U-value of 0.240 is used as a multiplier on the roof glazing conductance to model heat
retention during the night.
air gap (inches)
R-value
0.5
1.6
0.75
1.7
Table 14. Thermal Resistance (R-value) of air gaps. 5
1.5
1.8
3.5
2.0
12
2.5
18
3.0
Specifications for Ludvig Svensson, Thermal
Curtains (Aluminum/Polyester Strips)
Energy Diffuse Light
Type
saving transmission
Calculated
40%
84%
XLS 10 Firebreak
45%
78%
XLS 13 Firebreak
49%
65%
XLS 14 Firebreak
52%
53%
XLS 15 Firebreak
57%
43%
XLS 16 Firebreak
62%
34%
XLS 17 Firebreak
67%
24%
XLS 18 Firebreak
72%
17%
Table 15. Specifications for Ludvig Svensson, Thermal Curtains 6
Table 1 presents the specifications for thermal curtains from a large manufacturer. This analysis will assume
the heat curtain has an energy savings factor of 40%, based upon PG&E’s minimal requirement for
qualifying products, with a calculated diffuse light transmission of 84%. Figure 5 (in the appendix) illustrates
the calculations for arriving at the diffuse light transmission of a 40% energy savings factor heat curtain.
5
Based upon ASHRAE Fundamentals (page 25.4. Mean Temp of 50F, Temp difference of 10F, upward direction of heat flow.
Effective emittance of air space is assumed to be 0.2, based upon one side of air gap having thermal curtain with foil strips.
According to ASHRAE, moderate extrapolation for air spaces greater than 3.5 inches are permissible. See the appendix for
calculations.
6
See manufacturers’ website for further information: (http://www.ludvigsvensson.com/)
21
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Results
The following table presents the annual natural gas usage and savings, based upon weighted averages of the coastal climate zones (climate zones 1, 2,
3, 4 and 5) ; the weighted averages of the inland climate zones (climate zones 11, 12, and 13); and the weighted average of all zones together. Refer to
the appendix for data on square footage of greenhouses by county and climate zone. Because less than one percent of California greenhouse space is in
climate zone 16, this region has been ignored. As can be seen, while the gas usage is significantly different between the inland and the coastal
greenhouses, the savings are comparable. Refer to Table 21 in the appendix for annual electricity use savings for climate zones 3 and 12. The
electricity savings is from the fan energy consumed by the heaters. There is no peak demand savings. All savings in the following table are relative to
the shaded row in that group. For example the savings for alternative 5 “Alt 4 + 2nd layer heat curtain” are relative to alternative 3 and are equal to 1.04
therms/sf for coastal zones and 0.98 therms/sf for inland zones.
cz 01
cz 02
cz 03
cz 04
cz 05
Coastal zones,
weighted
averages
% of total greenhouse area (grouped by
coastal vs inland)
1.1%
1.3%
53.9%
28.3%
15.3%
% of total greenhouse area (all zones)
1.0%
1.2%
47.7%
25.1%
13.6%
Description
Use
Use
Use
Use
Use
Use
0
Double Inflated Poly w/ IR, 55F
0.59
0.44
0.34
0.32
0.24
1
Alt 0 + Single Heat Curtain
0.25
0.18
0.12
0.11
0.05
2
Alt 1 + 2nd layer heat curtain
0.15
0.08
0.06
0.04
0.01
0.05
0.27
0.17
0.12
0.05
0.11
0.35
0.05
0.28
2b
Alt 2 + 30% production increase
0.1
0.06
0.04
0.03
0.007
0.03
0.29
0.12
0.09
0.04
0.08
0.37
0.04
0.30
3
Double Inflated Poly w/ IR, 80F
2.71
2.05
2.28
1.92
2.02
2.14
N/A
2.15
2.3
1.59
2.13
N/A
2.14
N/A
4
Alt 3 + Single Heat Curtain
2.05
1.36
1.74
1.26
0.9
1.47
0.67
1.71
1.59
1.17
1.50
0.64
1.48
0.66
Coastal Climate Zones Usage
Alt
cz 11
cz 12
cz 13
Inland zones,
weighted
averages
100%
2.8%
74.3%
22.9%
100%
N/A
88%
0.3%
8.3%
2.8%
12%
100%
Saving
Use
Use
Use
Use
Saving
Use
0.32
N/A
0.54
0.49
0.32
0.45
N/A
0.34
N/A
0.11
0.21
0.27
0.22
0.12
0.20
0.25
0.12
0.22
Inland Climate Zones Usage
All zones,
weighted
averages
Saving
5
Alt 4 + 2nd layer heat curtain
1.68
1
1.36
0.93
0.48
1.10
1.04
1.39
1.22
0.9
1.15
0.98
1.11
1.03
5b
Alt 5 + 30% production increase
1.18
0.7
0.95
0.65
0.34
0.77
1.37
0.97
0.86
0.63
0.81
1.32
0.77
1.36
6
Double Inflated Poly no IR, 55F
0.78
0.59
0.47
0.46
0.35
0.45
N/A
0.7
0.65
0.43
0.60
N/A
0.47
N/A
7
Alt 6 + Single Heat Curtain
0.35
0.26
0.18
0.17
0.1
0.17
0.29
0.36
0.31
0.19
0.28
0.32
0.18
0.29
8
Alt 7 + 2nd layer heat curtain
0.2
0.13
0.09
0.07
0.02
0.08
0.38
0.22
0.17
0.09
0.15
0.45
0.08
0.39
8b
Alt 8 + 30% production increase
0.14
0.09
0.06
0.05
0.01
0.05
0.40
0.16
0.12
0.06
0.11
0.49
0.06
0.41
9
Alt 6 with IR film
0.59
0.44
0.34
0.32
0.24
0.32
0.13
0.54
0.49
0.32
0.45
0.15
0.34
0.13
10
Double Inflated Poly no IR,80F
3.24
2.5
2.74
2.49
2.48
2.63
N/A
2.57
2.78
1.95
2.58
N/A
2.62
N/A
11
Alt 10 + Single Heat Curtain
2.44
1.69
2.12
1.55
1.63
1.88
0.75
2.06
1.96
1.47
1.85
0.73
1.88
0.75
12
Alt 11 + 2nd Layer Heat curtain
1.97
1.22
1.65
1.15
0.74
1.37
1.26
1.66
1.49
1.13
1.41
1.17
1.37
1.25
12b
Alt 12 + 30% production
1.38
0.85
1.16
0.8
0.52
0.96
1.67
1.16
1.05
0.79
0.99
1.59
0.96
1.66
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cz 11
cz 12
cz 13
Inland zones,
weighted
averages
100%
2.8%
74.3%
22.9%
100%
88%
cz 01
cz 02
cz 03
cz 04
cz 05
Coastal zones,
weighted
averages
% of total greenhouse area (grouped by
coastal vs inland)
1.1%
1.3%
53.9%
28.3%
15.3%
% of total greenhouse area (all zones)
Coastal Climate Zones Usage
Inland Climate Zones Usage
All zones,
weighted
averages
N/A
12%
100%
1.0%
1.2%
47.7%
25.1%
13.6%
0.3%
8.3%
2.8%
Description
increase
Use
Use
Use
Use
Use
Use
Saving
Use
Use
Use
Use
Saving
Use
Saving
Alt 10 with IR film
2.71
2.05
2.28
1.92
2.02
2.14
0.49
2.15
2.3
1.59
2.13
0.45
2.14
0.49
30
Single layer polycarbonate, 55F
1.13
0.86
0.71
0.69
0.57
0.69
N/A
0.99
0.94
0.65
0.87
N/A
0.71
N/A
31
Alt 30 + Single Heat Curtain
0.53
0.42
0.31
0.3
0.2
0.29
0.39
0.55
0.48
0.32
0.45
0.43
0.31
0.40
32
Alt 31 + 2nd layer Heat Curtain
Alt 32 + 30% production
increase
0.32
0.23
0.16
0.15
0.06
0.14
0.54
0.34
0.29
0.16
0.26
0.61
0.16
0.55
0.23
0.16
0.12
0.1
0.05
0.11
0.58
0.24
0.2
0.12
0.18
0.69
0.11
0.60
33
Single layer polycarbonate, 80F
4.14
3.24
3.54
3.28
3.27
3.42
N/A
3.33
3.65
2.59
3.40
N/A
3.42
N/A
34
Alt 33 + Single Heat Curtain
3.12
2.26
2.82
2.28
2.23
2.57
0.85
2.73
2.66
2.02
2.52
0.88
2.56
0.86
35
Alt 34 + 2nd layer Heat Curtain
Alt 35 + 30% production
increase
2.55
1.55
2.2
1.72
1.05
1.88
1.54
2.19
2.03
1.57
1.93
1.47
1.89
1.53
1.78
1.08
1.54
1.2
0.74
1.32
2.11
1.53
1.42
1.1
1.35
2.05
1.32
2.10
Alt
13
32b
35b
Table 16. Annual Natural Gas Usage and Savings (therms per square foot)
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Appendix
Baseline Roof Material
While there is a significant difference in savings with applying heat curtains between double-inflated
roofs with and without IR film (see Figure 3), it is recommend that PG&E not adopt a separate tier for
these two cases. This recommendation is based upon the findings of the Greenhouse Baseline Study that
the majority of greenhouse roofs consist of double-inflated polyethylene with IR film (see Figure 4).
While this study was based upon a small sample size (22 greenhouse facilities), the findings are backed
up by anecdotal information from the vendors. Additionally, polyethylene roofs have a very short lifespan (3-5 years) compared to polycarbonate or acrylic (10-20+ years). By using the improved doublepolyethylene with IR film baseline for heat curtains incentives, PG&E could avoid incenting a more
generous amount for a roof which may be replaced within a few years.
double polycarbonate
6%
double acrylic
3%
single glass
15%
single
fiberglass
3%
single polycarbonate
18%
single polyethylene
3%
double polyethylene
9%
double polyethylene w/ IR
inhibiting film
43%
Figure 4. Distribution of Greenhouse Roof Materials (Source: PG&E Greenhouse Baseline Study)
Figure 5 illustrates the calculations for arriving at the diffuse light transmission of a 40% energy savings
factor heat curtain.
24
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LS Svensson XLS Firebreak Heat Curtain Series Diffuse Light
Transmission
85%
80%
75%
70%
65%
Diffuse Light Transmission
60%
55%
50%
45%
40%
35%
30%
25%
20%
y = -2.1975x + 1.7159
15%
10%
5%
0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
Energy Savings Factor
Figure 5. Graph of Ludvig Svensson XLS Firebreak Energy Curtains. Diffuse Light Transmission vs Energy
Savings Factor.
Climate Zones
The original Greenhouse Baseline Study conducted for PG&E stratified the data into three different
geographic regions: coastal, coastal valley, and inland valley. This aggregation was based upon
conversations with PG&E project manager John Blessent and PG&E meteorologist Woody Whitlatch.
The geographical segregation was accomplished by mapping the greenhouse locations with the California
Energy Commission climate zones (see Figure 10 in the appendix). Refer to Table 17 for the assignment
of the geographic regions by climate zone. Because less than one percent of California greenhouse space
is in climate zone 16, this region has been ignored.
Climate Zones
2, 4, and 12
1, 3, and 5
11 and 13
Category
Coastal Valley
Coastal
Inland Valley
Table 17. Grouping of Greenhouses by Climate Zones for the PG&E Greenhouse Baseline Study.
25
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If PG&E wishes to tier the greenhouse deemed savings by climate zones, we propose, for the sake of
simplicity, further aggregating the climate zones into two categories: into coastal (climate zones 1, 2, 3, 5
and 5) and inland (climate zones 11, 12, and 13).
Climate Zones
1, 2, 3, 4, and 5
11 12, and 13
Category
Coastal
Inland
Table 18. Proposed Grouping of Greenhouses by Climate Zones for the Deemed Savings Program.
Refer to Table 20 for a summary of the square footage of crops grown under cover (by County and
climate zones), based upon 2002 Census data.
Results indicate that natural gas usage is higher in climate zone 12, which may seem counter-intuitive.
However, climate zone 12 has colder temperatures than climate zone 3, as can be seen in Figure 6 and
Table 19. The data presented in Table 19 is from the California Energy Commission weather files for
climate zones 3 (Oakland is the reference city) and 12 (Sacramento is the reference city). The results
compare the number of heating degree days (HDD) and shows that climate zone 12 is colder than climate
zone 3. The weather files used in the analysis have been approved by the California Energy Commission.
CZ 03
(Oakland)
CZ 12
(Sacramento)
Average Daily Max Tdb
67.4
73.7
Average Daily Min Tdb
49.2
47.5
Avg. Annual Tdb
57.5
59.5
Annual Max Tdb
91
103
Annual Min Tdb
34
27
3107
3351
HDD (24 hours/65F)
Table 19. Summary of California Energy Commission Climate Zone HDD Calculations
26
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Min CZ 01(eg. Arcata )
Minimum Temperature by Climate Zone
Min CZ 02(eg. Santa Rosa )
Min CZ 03(eg. Oakland )
Min CZ 04(eg. Sunnyvale )
Min CZ 05(eg. Santa Maria )
60
Min CZ 11(eg. Red Bluff )
Min CZ 12(eg. Sacramento )
55
Min CZ 13(eg. Fresno )
Temp (deg F)
50
45
40
35
30
25
20
1
2
3
4
5
6
7
8
9
10
11
12
Month
Figure 6. Monthly Minimum Temperatures
Allocation of greenhouse square footage, Coastal zones
CZ 5
15%
CZ 1
1%
CZ 2
1%
CZ 4
28%
CZ 3
55%
Figure 7. Allocation of greenhouse square footage, coastal climate zones.
27
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Allocation of greenhouse square footage, Inland zones
CZ 11
3%
CZ 13
24%
CZ 12
73%
Figure 8. Allocation of greenhouse square footage, inland climate zones.
Allocation of greenhouse square footage, All Zones
CZ 12
8%
CZ 13 CZ 1
3% 1%
CZ 11
0%
CZ 2
1%
CZ 5
14%
CZ 3
48%
CZ 4
25%
Figure 9. Allocation of greenhouse square footage, all climate zones.
28
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County
Alameda
Butte
Contra Costa
El Dorado
Fresno
Humboldt
Kern
Lake
Lassen
Madera
Marin
Mendocino
Monterey
Napa
Nevada
Sacramento
San Benito
San Francisco
San Joaquin
San Luis Obispo
San Mateo
Santa Barbara
Santa Clara
Santa Cruz
Shasta
Siskiyou
Climate
Zone(s)
12
11/16
3/12
12/16
13/16
1
13/14/16
2
16
13/16
2/3
1/2/3/16
3/4
2
11/16
12
4
3
12
4/5
3
4/5/6
4
3
11/16
16
sq ft of
greenhouses
478,560
864,063
3,682,708
77,352
1,877,395
1,514,335
309,354
47,396
93,400
124,400
60,576
746,950
51,680,374
6,050
67,280
2,811,632
29,464
114,039
9,434,276
13,773,982
17,192,804
25,918,293
14,663,782
25,638,304
64,692
70,156
Solano
3/12
25,828
0.0%
Sonoma
2/3
5,148,121
2.8%
Stanislaus
12
299,478
0.2%
Sutter
11
113,000
0.1%
Tehama
11/16
34,310
0.0%
Trinity
2/11/16
3,046
Tulare
Yolo
13/16
12
3,591,573
316,948
0.0%
2.0%
0.2%
% of total
0.3%
0.5%
2.0%
0.0%
1.0%
0.8%
0.2%
0.0%
0.1%
0.1%
0.0%
0.4%
28.6%
0.0%
0.0%
1.6%
0.0%
0.1%
5.2%
7.6%
9.5%
14.3%
8.1%
14.2%
0.0%
0.0%
Table 20. Square Footage of Greenhouses by County and Climate Zones.
29
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Figure 10. California Climate Zones Map
Electricity Savings
The following table outlines the annual electricity use and annual electricity savings, per square foot, for
only climate zones 3 and 12. The electricity savings is from the fan energy consumed by the heaters.
There is no peak demand savings.
Alt
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Double Inflated Poly with IR Roof, 55F, CZ03 (Coastal) baseline
Alt 0 + Single-Layer Heat Curtain
Alt 1 + 2nd layer heat curtain
Double Poly Roof with IR, 80F, CZ03 (Coastal) baseline
Alt 3 + Single-Layer Heat Curtain
Alt 4 + 2nd layer heat curtain
Double Inflated Poly Roof no IR film, 55F, CZ03 (Coastal) baseline
Alt 6 + Single-Layer Heat Curtain
Alt 7 + 2nd layer heat curtain
Alt 6 with IR film
Double Inflated Poly Roof no IR Film, 80F, CZ03 (Coastal) baseline
Alt 10 + Single-Layer Heat Curtain
Alt 11 + 2nd Layer Heat curtain
Alt 10 with IR film
Annual Electricity Use
(kWh/sq ft)
0.16
0.12
0.11
0.50
0.41
0.34
0.19
0.14
0.12
0.16
0.58
0.47
0.39
0.50
30
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Annual Electricity Savings
(kWh/sq ft
N/A
0.04
0.01
N/A
0.09
0.07
N/A
0.05
0.02
0.03
N/A
0.11
0.08
0.08
February 5, 2008
Alt
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
Annual Electricity Use
(kWh/sq ft)
Annual Electricity Savings
(kWh/sq ft
0.51
0.48
0.49
0.63
0.53
0.48
0.51
0.48
0.48
0.51
0.70
0.58
0.51
0.63
N/A
0.03
-0.01
N/A
0.10
0.05
N/A
0.03
0.00
0.00
N/A
0.12
0.07
0.07
0.23
0.16
0.13
0.72
0.59
0.48
N/A
0.07
0.03
N/A
0.13
0.11
0.52
0.46
0.46
0.82
0.67
0.58
N/A
0.06
0.00
N/A
0.15
0.09
BLANK
Double Poly with IR roof, 55F, CZ12 (Inland) baseline
Alt 15 + Single-Layer Heat Curtain
Alt 17 + 2nd layer heat curtain
Double Poly Roof with IR, 80F, CZ12 (Inland) baseline
Alt 18 + Single-Layer Heat Curtain
Alt 19 + 2nd Layer Heat curtain
Double Inflated Poly Roof no IR film, 55F, CZ12 (Inland) baseline
Alt 21 + Single-Layer Heat Curtain
Alt 22 + 2nd Layer Heat curtain
Alt 21 with IR film
Double Inflated Poly Roof no IR film, 80F, CZ12 (Inland) baseline
Alt 25 + Single-Layer Heat Curtain
Alt 26 + 2nd Layer Heat curtain
Alt 25 with IR film
BLANK
Single layer polycarbonate roof, 55F, Coastal (CZ 3) baseline
Alt 30 + Single Heat Curtain
Alt 31 + 2nd layer Heat Curtain
Single layer polycarbonate roof, 80F, Coastal (CZ 3) baseline
Alt 33 + Single Heat Curtain
Alt 34 + 2nd layer Heat Curtain
BLANK
Single layer polycarbonate roof, 55F, Inlandl (CZ 12) baseline
Alt 37 + Single Heat Curtain
Alt 38 + 2nd layer Heat Curtain
Single layer polycarbonate roof, 80F, Inland (CZ 12) baseline
Alt 40 + Single Heat Curtain
Alt 41 + 2nd layer Heat Curtain
Table 21. Electricity Use and Savings Results
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Work Paper PGECOAGR101, Revision 0
Prepared by Green Building Studio for Pacific Gas & Electric Company
Greenhouse Thermal Curtains PGECOAGR101 R0.doc
February 5, 2008
References
1
The PG&E Greenhouse Baseline Study found that the greatest majority of crop types grown within
PG&E service territory greenhouses is cut flowers (47%). This figure is based upon 2002 Census data.
According to Bond, T.E. et. al. 1985. Reducing Energy Costs in California Greenhouses. University of
California Cooperative Extension. (http://ohric.ucdavis.edu/Newsltr/GreenhouseEnergy.pdf) typical
cut flowers can be grown at 55F or less.
2
Per Peter Fryn of System USA Inc., a tented, double system would cost $2.60 and a double flat system
would cost $2.10 installed
3
Copied from PG&E “Energy Efficiency Rebates For Your Business” brochures.
http://www.pge.com/includes/docs/pdfs/catalogs/biz_catalog.pdf
4
Bartok, John W., Jr. 2001. Energy Conservation for Commercial Greenhouses.NRAES-3. Ithaca, NY:
Natural Resource, Agriculture, and Engineering Service.
5
Source of characteristics, the manufacturer’s website.
(http://www.ludvigsvensson.com/Default.asp?LocationID=1&LanguageID=3)
6
Based upon ASHRAE Fundamentals (page 25.4. Mean Temp of 50F, Temp difference of 10F, upward
direction of heat flow. Effective Emittance of air space is assumed to be 0.2, based upon one side of air
gap having thermal curtain with foil strips. According to ASHRAE, moderate extrapolation for air spaces
greater than 3.5 inches are permissible.
7
Southern California Edison. December 2005. 2004-2005 Database for Energy Efficiency Resources
(DEER) Update Study Final Report. Prepared by Itron, Inc., Vancouver, Washington.
http://www.energy.ca.gov/deer/
8
Greenhouse Baseline Study, prepared for PG&E by Green Building Studio, December 2005. This
reference is included as Attachment #1.
9
Greenhouse Baseline Study, prepared for PG&E by Green Building Studio, December 2005. This
reference is included as Attachment #1.
10
Peter Fryn of System USA Inc. is a major vendor to greenhouse owners. His experience is that the
baseline roof material for coastal greenhouses is single-layer Dynaglas (Polycarbonate) and not doubleinflated polyethylene. Our 2005 baseline study for PG&E found that of the 20 greenhouse facilities in
coastal locations interviewed for the study, the largest number (7) had double-polyethylene roofs, 5 had
glass roofs, and 3 had single polycarbonate roofs. The remaining roof types were distributed among other
materials.
11
Hoogeboom, John, Hill, John, and Addison, Marlin. 2004. Savings By Design Whole Building
Analysis Summary: Gilroy Young Plant Nursery. PG&E Report.
12
Ibid
32
Work Paper PGECOAGR101, Revision 0
Prepared by Green Building Studio for Pacific Gas & Electric Company
Greenhouse Thermal Curtains PGECOAGR101 R0.doc
February 5, 2008
13
Bartok, John W., Jr. 2001. Energy Conservation for Commercial Greenhouses.NRAES-3. Ithaca, NY:
Natural Resource, Agriculture, and Engineering Service.
33
Work Paper PGECOAGR101, Revision 0
Prepared by Green Building Studio for Pacific Gas & Electric Company
Greenhouse Thermal Curtains PGECOAGR101 R0.doc
February 5, 2008